When carrying out chemical or biochemical analyses, assays, syntheses, or preparations one performs a large number of separate manipulations on the material or component to be assayed, including measuring, aliquotting, transferring, diluting, mixing, separating, detecting, etc. Microfluidic technology miniaturizes these manipulations and integrates them so that they can be performed within one or a few microfluidic devices.
For example, methods of performing dilutions in microfluidic devices were described in U.S. Pat. No: 5,869,004, by Parce and Kopf-Sill, “Methods and Apparatus for in Situ Concentration and/or Dilution of Materials in Microfluidic Systems.” These methods successively draw off and add materials to microfluidic channels to serially dilute materials. The methods allow large accurate dilutions to be performed within the microscale environment.
For some bioassays, a constant flow of material is useful to maintain a fixed assay reaction time. Therefore, the ability to modulate a flow rate and obtain constant incubation and reaction times in a microfluidic system when performing dilutions would be useful to the integration of fluidic sample and reagent manipulations in a microfluidic assay format. In addition, a constant flow rate, e.g., in a microfluidic device with a single pressure source, would help to reduce the reagent usage for reagents added after the dilutions have been made.
Another technique that would be useful to integrate into a microfluidic format would be the ability to measure a sample at different concentrations simultaneously, to concurrently perform reactions at varying concentrations, and/or to test one sample concurrently versus a panel of different reagents.
Improved methods for controlling flow rates during dilutions and multiple concentration assays are, accordingly desirable, particularly those which take advantage of high-throughput, low cost microfluidic systems. The present invention provides these and other features by providing high throughput microscale systems for dilutions, reduced reagent consumption, multiple concentration measurements, and many other features that will be apparent upon complete review of the following disclosure.